[aprssig] ***SPAM*** Re: APRS Cron Object Injector

KF4LVZ aprssigZbr6 at acarver.net
Sun Mar 22 21:55:06 CDT 2015


Several flavors of cron daemons do allow for specifying an offset such
that the starting time is not on the zeros[1].  Without running an
entire script it's possible to have varying start times and reduce the
load.  Yours just happens to randomize it at each execution which is an
interesting solution.

For any user that does need regularity in the beacon (without a random
delay) then instead of specifying "*/20 * * * *" to run every twenty
minutes you can change the minute field to another representation so
that a fixed delay is inserted pushing the repetition to some other
sequence of minutes.  The two most common are (for the minutes field but
it applies to all):

7-59/20 (one implementation)
*/20+7 (another implementation)

Both of these attempt to start the script at 7 minutes past the hour and
every 20 minutes thereafter.  Change the 7 to some other number to have
a distributed series of executions.  One possibility would be to take
the numeric equivalent of the last letter in the callsign modulo 10.


On 2015-03-22 19:10, Kenneth Finnegan wrote:
> While helping am aprx user debug an RF-gate issue this week, it came
> to my attention that some users beacon objects into APRS using cron
> (The Unix task scheduler). This is far from ideal, since it means
> these objects are only being sent to APRS-IS and not being injected
> into the actual RF LAN, but the fatal flaw I see is that none of the
> cron scripts I've found online implement any form of dithering.
> 
> Even when an RF-gate is correctly configured to gate objects, since
> these objects are ALL beaconed on the top of the interval, RF-gates
> are dropping objects due to rate limiting.
> 
> In the ideal world we'd have users using more sophisticated daemons
> than cron to beacon objects for local info, but I decided to write my
> own sample script to match the cron job pattern:
> 
> https://github.com/PhirePhly/aprs_cron_injector
> 
> To use, simply make a unique local copy of the script for each object,
> open it in an editor and fill in the fields at the top of the script,
> and schedule it to run at your desired interval. The goal here is to
> be minimalist and easy to get people started in beaconing APRS
> objects.
> 
> The script makes a good attempt at performing error checking, then
> delays the beacon a random <5 minute interval to reduce the peak
> bandwidth requirement for the APRS network.
> 
> Converting the script for other uses such as bulletins should be
> relatively easy (just edit the OBJ_STRING definition towards the
> bottom), but serious users should move to an actual APRS daemon such
> as aprx (https://github.com/PhirePhly/aprx).
> --





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